[Horace]

If you're on 10meg and only getting up to 5meg or less consistantly the obvious solution is to downgrade to 4meg and save some cash. Hitting NTL where it hurts (in the pocket) is far more likely to succeed than complaining about it.
Not that I'm saying you shouldn't complain, but if all avenues have been gone down and you're still not getting full speeds regularly that it seems the obvious answer.